Posted by Andy on Sunday, December 8, 2013 at 12:30pm.
A ruler stands vertically against a wall. It is given a tiny impulse at θ=0∘ such that it starts falling down under the influence of gravity. You can consider that the initial angular velocity is very small so that ω(θ=0∘)=0. The ruler has mass m= 100 g and length l= 35 cm. Use g=10 m/s2 for the gravitational acceleration, and the ruler has a uniform mass distribution. Note that there is no friction whatsoever in this problem. (See figure)
(a) What is the angular speed of the ruler ω when it is at an angle θ=30∘? (in radians/sec)
ω=
unanswered
(b) What is the force exerted by the wall on the ruler when it is at an angle θ=30∘? Express your answer as the x component Fx and the y component Fy (in Newton)
Fx=
unanswered
Fy=
unanswered
(c) At what angle θ0 will the falling ruler lose contact with the wall? (0≤θ0≤90∘; in degrees) [hint: the ruler loses contact with the wall when the force exerted by the wall on the ruler vanishes.]
θ0=

physics I'M STUCK PZL HELP  Anonymous, Sunday, December 8, 2013 at 1:25pm
yes please.. that's the only question where I'm stuck too..

physics I'M STUCK PZL HELP  Teresa, Sunday, December 8, 2013 at 1:26pm
Me too!!!

physics I'M STUCK PZL HELP  ROMA, Sunday, December 8, 2013 at 2:15pm
Hi Teresa, can you do rocket problem me pls?

physics I'M STUCK PZL HELP  Teresa, Sunday, December 8, 2013 at 2:23pm
p: percentage (4.5% is burned in 155s)
m:mass of rocket
u:fuelspeed in meter/s!
v=u*ln(1/(1p))=1500*ln(1/0.955)
a=v/t = 69.065/155= 0.4455

physics I'M STUCK PZL HELP  ROMA, Sunday, December 8, 2013 at 3:18pm
Hi Teresa, in my problem, question says The rocket burns 10 % of its mass in 290 s (assume the burn rate is constant).
What is the speed of the rocket after a burn time of 145.0 s?
How did you find 4.5% is burned in 155 sec? Pls.
Thank you very much

physics I'M STUCK PZL HELP  Teresa, Sunday, December 8, 2013 at 3:58pm
because they ask you for half of the time,
so in your case in 145 it gets burned 5% in 145 seconds

physics I'M STUCK PZL HELP  ROMA, Sunday, December 8, 2013 at 8:17pm
Thank you very much Teresa. I got green check. Now time for rular one..

physics I'M STUCK PZL HELP  anon, Sunday, December 8, 2013 at 8:42pm
in the equation above what is the "ln"?

physics I'M STUCK PZL HELP  ROMA, Sunday, December 8, 2013 at 8:52pm
"ln" is like log..it is in your calculator

physics I'M STUCK PZL HELP  anon, Sunday, December 8, 2013 at 9:00pm
is the "u" the ejected fuel in m/s instead of km/s?

physics I'M STUCK PZL HELP  kumar, Monday, December 9, 2013 at 3:15am
hai Teresa can u help me for this Rocket question i don't know how to get 0.955 in the above ans !
Consider a rocket in space that ejects burned fuel at a speed of vex= 2.0 km/s with respect to the rocket. The rocket burns 11 % of its mass in 250 s (assume the burn rate is constant).
(a) What is the speed v of the rocket after a burn time of 125.0 s? (suppose that the rocket starts at rest; and enter your answer in m/s)
v=
unanswered
(b) What is the instantaneous acceleration a of the rocket at time 125.0 s after the start of the engines?(in m/s2)
a=
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